Polysulfide as a novel chemical agent to solidify/stabilize lead in fly ash from municipal solid waste incineration

Polysulfide was produced and tested for use as an inexpensive chemical agent for the solidification/stabilization of lead in fly ash, generating little hydrogen sulfide gas. According to the equations S(n)(2-)-->S+S(n-1)(2-) and S(n)(2-)+H(+)-->HS(-)+S(n-1), this agent was expected to achieve long-term stability of disposed Pb. The leachate concentration of Pb in fly ash after sulfide treatment showed a decrease-increase-decrease trend. We also compared Pb leaching behavior from an aging/weathering experiment to thermodynamic modeling using the database from the Geochemist's Workbench software. Thermodynamic modeling indicated the tendency that when the precipitate was formed in the order of PbO, PbCO(3).PbO, and PbCO(3), the total concentration of soluble Pb will be lowered. The leaching curve of Pb in fly ash without a lime slurry injection system was close to PbO, whose activity was initially near 1, but when leaching time increased, it shifted to that of PbCO(3).PbO, before finally ending at that of PbCO(3). However, Ca(OH)(2) sprayed on fly ash interfered with the carbonation process of Pb.